1. Field of the Invention
The invention in general relates to a rotary tool for drilling, and particularly for trepanning procedures.
2. Description of the Prior Art
Trepanning operations involve the removal of a disk or cylindrical core from a workpiece. A diversity of drill arrangements exists for this purpose and generally include a cylindrical cutter portion having some sort of abrading material at the lower margin thereof, together with a coolant fluid for flushing away drilled material from the workpiece.
For many applications the existing drills are entirely satisfactory. For ultraprecision drilling operations however, a need exists for a drill apparatus which can initiate a cut into a relatively hard material without progressively chipping the surface thereof and without causing a tapered hole.
To achieve this precision drilling, the drilling procedure requires the application of a protective plate overlay to the workpiece in order to stabilize the drill cutting operation and to absorb chipping so as to protect the surface finish of the workpiece. After the cutting operation and after the disk or cylindrical core has been removed, an ultrafine diamond coated tool is utilized to provide an ultrasmooth finish on the wall surface of the hole or removed piece of material.
One type of workpiece which occasionally requires a trepanning operation is a piezoceramic transducer having a surface coated with a thin silver layer acting as an electrode. Silver is relatively soft and under high speed operation of the core drill results in a plugging up of the drill's cutting surface in a manner that prevents further free cutting, as buildup of the plug is thicker than the abrading material depth. To prevent this, conventional practice requires the removal of the silver electrode prior to cutting, and the subsequent deposition of the electrode after cutting.
The core drilling apparatus of the present invention eliminates the requirement for an overlay application when drilling hard materials and, when drilling into soft materials does not plug up, thereby eliminating the need for removing relatively soft surfaces such as in electrode transducer workpieces.